The present invention relates to positron tomographs consisting of one or more detector rings, and more particularly it relates to obtaining high resolution in such a tomograph by sampling with the tomograph in a first position and then taking at least one other sample with the tomograph in another position in the same plane.
Rapid sequence imaging is an inherent advantageous characteristic of stationary positron tomographs wherein detection is accomplished by means of scintillation within crystals arranged in a ring around the subject to be examined. This rapid sequence imaging characteristic makes such instruments valuable diagnostic tools in the practice of medicine. However, because of insufficient linear sampling in stationary ring tomographs, the intrinsic resolution of the individual crystal detectors is not achieved. Resolution of these instruments therefore needs improvement. The greater the number of crystals, the better the resolution of the instrument. Therefore, a large number of crystal detectors are used in such instruments, along with complex electronic circuits for each detector.
In order to maximize the number of crystals in each ring and thereby enhance the resolution of the instrument, efforts have been made to closely pack the crystals. Such efforts are generally believed to have been carried to practical limits. Consequently, various other schemes have been suggested and tried to improve resolution. Notably, such schemes include sampling with the ring in a first position and then sampling at least one more time with the ring in a second position. There can also be additional positioning and sampling to further increase the resolution.
Various multiple positioning sampling schemes are described in the following references, all of which are incorporated herein by reference:
1. Phelps ME, Hoffman EJ, Mullani NA, et al: "Application of annihilation coincidence detection to transaxial reconstruction tomography", J. Nucl. Med. 16: 210-224, 1975. PA1 2. Mullani NA, Ter-Pogossian MM, Higgins CS et al: "Engineering aspects of PETT V", IEEE Trans. Nucl. Sci., NS-26: No. 2 2703-2706, 1979. PA1 3. Ter-Pogossian MM, Mullani NA, Hood J, et al: "A multislice positron emission computed tomograph (PETT IV) yielding transverse and longitudinal images", Radiology, 128: 477-484, 1978. PA1 4. Williams CW, Crabtree MC, and Burgiss SG: "Design and performance characteristics of a positron emission computed axial tomograph--ECAT-II", IEEE Trans. Nucl. Sci., NS-26: No. 1, 619-627, 1979. PA1 5. Bohm C. Eriksson L. Bergstrom M, et al: "A computer assisted ring detector positron camera system for reconstruction tomography of the brain", IEEE Trans. Nucl. Sci., NS-25: No. 1, 624-637, 1978. PA1 6. Brooks RA, Sank VJ, Talbert AJ, et al: "Sampling requirements and detector motion for positron emission tomography", IEEE Trans. Nucl. Sci., NS-26: No. 2, 2760-2763, 1979. PA1 7. Tanaka E. Nohara N, Yamamoto M, et al: "Positology - the search for suitable detector arrangements for a positron ECT with continuous rotation", IEEE Trans. Nucl. Sci., NS-26: No. 2, 2728-2731, 1979. PA1 8. Nohara N. Tanaka E, Tomitani T, et al: "Positologica: A positron ECT device with a continuously rotating detector ring", IEEE Trans. Nucl. Sci., NS-27: No. 3, 1128-1136, 1980. PA1 9. Cho ZH, Hong KS, Ra JB, et al: "A new sampling scheme for the ring positron camera-dichotomic ring sampling", IEEE Trans. Nucl. Sci., NS-28: No. 1, 94-98,1981.
In the foregoing references, various multiple positioning and sampling approaches to overcome the resolution limitation of stationary detector ring tomographs are described. These approaches include: scan-rotation motion of the ring, circular wobble, rotation of nonuniformly spaced detectors, and rotation of half-rings about the center.
In all of the foregoing approaches there are serious disadvantages. Each approach requires at least four and up to 100 positions to provide improved sampling at all angles with attendant mechanical and electrical complexity to achieve such motion accurately. Each approach also requires extensive electronic circuitry changes, and computer and computer programming changes to adapt a stationary, detector ring to the approach.